The present invention is directed to a method and system for transmitting information via the radio interface between subscriber equipment and a network.
As known, a radio interface exists between subscriber equipment and a network equipment in cellular mobile radiotelephone networks. A radio link for which the three lowest layers (layers 1 through 3) of the ISO layer model are provided is made available for information transmission in both transmission directions. The lowest layer (layer 1) supports the information transmission via physical radio channels, whereas logical radio channels such as, for example, traffic channels for the transmission of user information and control channels for the transmission of signalling information are imaged onto the physical radio channels in the connection protection layer (layer 2) lying thereabove. The connection protection layer serves the purpose of protecting the information transmission in the network layer (layer 3) lying thereabove. The logical radio channel can be differently constituted in physical terms in different cellular mobile radiotelephone networks. For example, the logical radio channel comprises a packet-switched satellite network with a plurality of network nodes or physical transmission channels combined to form bundles in a terrestrial or satellite-supported mobile radiotelephone network. Independently of the respective physical constitution, the logical radio channel is set up by the signalling via the radio interface.
A protection protocol for the radio connection is used for protected information transmission. A protection protocol (radio link protocol) for a cellular mobile radiotelephone network according to the GSM standard (Global System for Mobile Communication) is known from GSM Recommendation 04.22, Version 5.5.0, October 1995. An information protection connection can thereby be set up or reset by the subscriber equipment or the network equipment in order to subsequently broadcast a plurality of transmission frames, each of which respectively comprises a header field and an information field, via the radio interface with the radio channels in an information transmission phase. The transmission frames broadcast in the information transmission phase are usually numbered, whereby the numbering always begins with the same prescribed starting value, for example the value zero, after every setup or resetting of the information protection connection.
Given the different physical characteristic of the logical radio channel, different delays of the individual transmission frames can occur on the transmission link. When individual transmission frames are overtaken in terms of time, this leads to the fact that the frames do not arrive at the receiver in the sequence in which they were transmitted. After the setup or resetting of the information protection connection, a reliable decision cannot be made as to whether an arriving transmission frame was still set before or already sent after the setup or resetting. This potentially leads to an unnoticed loss of transmitted information and/or to an unnoticed generation of new information. The function of the protection protocol for protected information transmission is thus not assured in every instance.